This invention relates-generally to processes and equipment for fining and polishing ophthalmic lenses and more particularly concerns conformal tools and the processes and apparata associated in the operation thereof.
The ability to accurately grind ophthalmic lenses to asymmetrical geometries specifically suited to the individual is relatively new in the ophthalmic lens industry. As a result, little work has been done in the development of fining and polishing tools to increase the accuracy of the fining/polishing operation.
In the past, fining/polishing tools provided a global conformance to the lens. That is, a separate tool was used for every possible contour of lens and, for each lens, the proper tool had to be selected and mounted on the fining/polishing apparatus. However, the recent development of more accurate lens surfacing equipment mandates improvement in the fining/polishing equipment since presently known fining/polishing equipment would damage the accurate geometries made possible by the new equipment. With the advent of improved lens conforming equipment, modern lenses exhibit wide variations in face curvature. For example, in aspheric lenses, in the progression in length of radius to the curvature of the lens face, the radius to the extremity of the lens is normally greater than the radius to the center of the lens so that the lens flattens towards its extremities. However, in modern lenses, the progression may be decreasing and/or increasing so that the face of the lens might change from a convex to a concave and back to a convex condition. Fining/polishing such a lens with presently known equipment generally results in the loss of the correct geometry of the lens. Furthermore, while spherical and aspherical lenses are generally rotationally symmetrical, progressive and toric lenses can now be ground which do not meet this condition. While some work has been done in the development of conformal tools which can be used to fine/polish a variety of symmetrical, spherical and aspherical lenses, no equipment has been presently developed which will permit a single or minimal number of fining/polishing tools to conform to all contours of lenses including toric lenses.
While some conformal tool development work has been done, no such tool is presently available which is not progressively incremented. That is, conformance is accomplished in incremental diopter ranges so that the tool does not accurately conform progressively at any position of a lens contour. Thus, the fining/polishing process can adversely effect the accuracy of the lens geometry.
One presently known conformal tool employs air pressure under the control of the operator in the conformal tool to control the degree of conformance to the lens. However, the use of air pressure or hydraulic pressure under operator control introduces inaccuracy into the system. In addition, the face of the tool tends to buckle and lose its integrity with the lens surface, introducing further error into the system. In addition, the tool is oriented so that the lens to be fined/polished is above the tool. As a result, gravitational pulls cause further problems with both the tool and the polishing medium. Furthermore, while the tool is mounted on a fixed axis, the lens is mounted on a floating axis, permitting a flopping action between the lens and the finer/polisher, causing further problems in accuracy and also damage to the finer/polisher. In fact, the finer/polisher is required to be greater than half the diameter of the lens or the lens would drop off the tool should it oscillate past the tool center. Also, in one known conformal tool, while the tool rotation is controlled with respect to both rotating rpm and orbital rpm, the lens is rotated at a multiple of the tool rotation and the lens rotational speed is not otherwise controllable. This restricts control of the abrasive aggressiveness of the device.
Other problems with known conformal tools include the requirements of alignment or coincidence of the center line of the tool with the center line of the lens, resulting in lower angular velocities being focused toward the center line and higher angular velocities being focused outwardly therefrom, causing a distortion of the lens. Perhaps most significantly, even in known conformal tools, conformance to the lens is still global rather than local.
It is, therefore, an object of this invention to provide a fining/polishing tool affording greater local conformance than has been heretofore available. It is also an object of this invention to provide a fining/polishing tool having computer controlled parameters of operation that may be varied and optimized based on selection of lens material and geometry. Another object of this invention is to provide a conformal tool which resists buckling and maintains its integrity in conformance to the lens. Another object of this invention is to provide a conformal tool that does not require parallel or coincident arrangement of the tool and lens axes of rotation. Still another object of this invention is to provide a conformal tool that does not require pneumatic or hydraulic pressure to achieve conformance to a lens. Yet another object of this invention is to provide a conformal tool which is usable for both fining and polishing. Another object of this invention is to provide a conformal tool operating apparatus which does not require that the tool be greater than one-half the diameter of the lens. Another object of this invention is to provide a conformal tool operating apparatus which requires no operator manual control during its operation. It is a further object of this invention to provide a conformal tool operating apparatus which facilitates variation in the angular alignment of the tool axis in relation to the lens axis. It is a further object of this invention to provide a conformal tool operating apparatus which facilitates the transverse displacement of the tool in relation to the rotational axis of the lens.